1. Field of the Invention
The present invention relates to semiconductor coating equipment. More particularly, the present invention relates to photoresist supply apparatus for dispensing photoresist onto a substrate such as a semiconductor wafer.
2. Description of the Related Art
The processes involved in the manufacturing of semiconductor devices can be generally classified as fabrication, assembly and test processes. The fabrication processes include supply, diffusion, photolithography, etching and thin film-forming processes. These processes are carried out selectively and repeatedly on a wafer to construct an electrical circuit on the wafer.
In the photolithography process, an oxide film is formed on the surface of a polished silicon wafer to protect a surface of the wafer, liquid photoresist is dispensed onto the oxide film, and then the wafer is rotated at a high speed to form a uniform coating of the photoresist on the wafer. Next, the wafer is selectively exposed so that a portion of the layer of photoresist undergoes a photo-chemical reaction, whereby a virtual image is transcribed onto the photoresist. Next, the photoresist is developed to form a pattern corresponding to the virtual image. Then, a thin film that exists below the patterned photoresist is etched by gas or chemicals, using the photoresist pattern as a mask, to in turn pattern the thin film. In this photolithography process the photoresist plays a very important role in the forming of the pattern. In particular, the precision of the line width and/or the CD (critical dimension) of the pattern depends on the thickness and uniformity of the layer of photoresist formed on the wafer.
A prior art apparatus for forming a uniform layer of photoresist on a wafer includes a storage tank for storing the photoresist, a dispensing tube for dispensing the photoresist onto a wafer, a supply line connecting the storage tank to the dispensing tube, a valve associated with the storage tank, and a main sensor installed adjacent the valve. The apparatus also includes an auxiliary sensor connected between the valve and the dispensing tube for sensing a residual amount of photoresist in the supply line. The auxiliary sensor is provided to prevent bubbles from being undesirably entrained in the photoresist when the main sensor is operating erroneously.
Also, an apparatus for forming a uniform layer of photoresist on a wafer is disclosed in U.S. Pat. No. 6,332,924 B1. This conventional photoresist supply apparatus is provided with a plurality of bottles containing the photoresist. When photoresist in one bottle is exhausted, the bottle is replaced. FIG. 1 illustrates this prior art photoresist supply apparatus.
The photoresist supply apparatus includes first and second photoresist bottles 10 and 30, first and second gas supply pipes 12 and 32, first and second gas supply valves 11 and 31, first and second photoresist supply pipes 14 and 34, first and second trap tanks 16 and 36, a third photoresist supply pipe 44, a nozzle 46, first and second level sensors 18 and 38, first and second discharge pipes 22 and 42, and first and second drain valves 20 and 40.
The first and second photoresist bottles 10 and 30 store the same type of photoresist solution.
The first and second gas supply pipes 12 and 32 are connected to the first and second photoresist bottles 10 and 30, respectively, to supply N2 purge gas to the bottles. The first and second gas supply valves 11 and 31 are installed in the first and second gas supply pipes 12 and 32. Each of the valves 11 and 31 can be switched between respective positions at which the N2 purge gas is supplied to or cut off from the respective bottle 10, 30.
The first and second photoresist supply pipes 14 and 34 are connected to upper parts of the first and second photoresist bottles 10 and 30, respectively, to supply photoresist solution. The first and second trap tanks 16, 36 are, in turn, connected to the first and second photoresist supply pipes 14 and 34 to receive photoresist supplied from the first and second photoresist bottles 10 and 30. The third photoresist supply pipe 44 is connected to the first and second trap tanks 16 and 36 to supply the photoresist from the first and second trap tanks 16 and 36 to the nozzle 46. The nozzle 46 sprays the photoresist, supplied through the third photoresist supply pipe 44, onto a wafer.
The first and second level sensors 18 and 38 are installed on the first and second trap tanks 16 and 36, respectively, to sense when the tanks 16 and 36 are low and hence, when the bottle 10 and 30 are empty.
The first and second discharge pipes 22 and 42 are connected to upper parts of the first and second trap tanks 16 and 36, respectively, to discharge photoresist from the first and second trap tanks 16 and 36. The first and second drain valves 20 and 40 are installed in the first and second discharge pipes 22 and 42. The valves 20 and 40 can each be switched between positions at which the photoresist solution is discharged from a tank 16, 36 through the discharge pipe 22, 42 connected thereto or the discharge is cut off.
The operation of the apparatus will be described, referring again to FIG. 1.
First, when the process is to be carried out using photoresist solution contained in the second photoresist bottle 30, a worker opens the second drain valve 40 and the second gas supply valve 31. At this time, the N2 purge gas is supplied through the second gas supply pipe 32, thereby pressurizing the second photoresist bottle 30. Accordingly, the photoresist solution is supplied to the second trap tank 36 through the second photoresist supply pipe 34 to fill the second trap tank 36 with the photoresist. Once the photoresist solution fills the trap tank 36, and the photoresist solution starts to discharge through the discharge pipe 42, the worker closes the second drain valve 40. Then, the photoresist solution in the trap tank 36 is supplied by a pump (not shown) to the nozzle 46 through the third supply pipe 44, whereby the photoresist solution is sprayed onto the wafer.
At some time during this deposition process the second level sensor 38 senses, via the level of photoresist in the tank 36, that the second photoresist bottle 30 is empty. When the second photoresist bottle 30 is detected as being empty, the worker opens the first drain valve 20 and the second gas supply valve 11. At this time, the N2 purge gas is supplied through the first gas supply pipe 12, thereby pressurizing the first photoresist bottle 10. Accordingly, the photoresist solution in the first photoresist bottle 10 is supplied to the first trap tank 16 through the first photoresist supply pipe 14 to fill first trap tank 16. Once the first trap tank 16 is filled, and the photoresist solution starts to discharge through the discharge pipe 22, the worker turns off the first drain valve 20.
As described above, the conventional photoresist supply apparatus is operated by a worker. This operation can be wasteful because various amounts of the photoresist, determined by each worker, are discharged during the filling of the trap tanks 16 and 36.
Furthermore, the conventional photoresist supply apparatus may cause a process defect when one of the level sensors malfunctions. In this case, an empty state of a photoresist bottle is not sensed once the photoresist in a trap tank is exhausted. Accordingly, the operation is not switched over to use the photoresist contained in the other photoresist bottle, nor is the empty bottle exchanged.